2.1.2 Biological molecules

Question 1

describes H-bonding

Answer 1

a slightly +ve hydrogen is attached to a slightly -ve oxygen in a neighboring molecule

Question 2

the property of water which allows some insects to walk on its surface

Answer 2

cohension

Question 3

a molecule of amylopectin is made up of

Answer 3

α-glucose molecule joined by 1-4 and 1-6 glycosidic bonds

Question 4

why is cellulose a good substance for maintaining cell wall structure

Answer 4

straight and forms many H-bonds between fibres

Question 5

molecular formula for a hydrogen carbonate ion

Answer 5

‎HCO3-

Question 6

what the results that indicated the presence of lipids in an emulsion test

Answer 6

cloudy emulsion

Question 7

which group of proteins do all enzymes belong to

Answer 7

globular

Question 8

describes a triglyceride componants

Answer 8

3 fatty acids joined to a glycerol molecule

Question 9

name the 3 parts of amino acids

Answer 9

• an amino( NH2) group
• a variable R-group (CR)
• a carboxyl (COOH) group

Question 10

describe bond that is formed when two amino acids are joined together

Answer 10

peptide bond

• formed between amine group and carboxyl group (of another)
• H (from amine) combines with OH (from carboxyl)
• condensation, water produced

Question 11

Describe ways in which the physical properties of water allow organisms to survive over
a range of temperatures.

Answer 11

• water beneath ice so is insulated, remains liquid
• aquatic organisms, do not freeze, can still swim
• effective solvent ;
• medium for reactions, (internal) transport medium / able to dilute toxic substances ;
• cohesion / adhesion ;
• example of cohesion / adhesion, in living organism ; C2 e.g. transpiration stream / apoplast movement

T1 surface tension ;
T2 habitat for (named) invertebrates ; T2 ACCEPT insects IGNORE animals
P1 transparent ;
P2 allows underwater photosynthesis ; P2

D1 idea of high density ; D1 IGNORE references to viscosity
D2 allows flotation / support ;
U organisms can still obtain, oxygen / (named) minerals / food /
carbon dioxide, from water

Question 12

Describe how these R groups can interact to determine the tertiary structure of a protein.

Answer 12

1 some R groups, attract / repel ;
2 disulfide bridges between, cysteine / SH / S (atoms) ;
- H -bonds ;
- ionic bonds between, oppositely charged / + and -, R groups ;
- hydrophilic R groups, on outside of molecule / in contact withwater (molecules) ;
- hydrophobic R groups, on inside of molecule / shielded from water (molecules) ;